Natural Invulnerability

From AmtWiki

A form of Monster "Armor."

Description from the Dor Un Avathar X

A skintight layer of overall (nonsectional) protection. Each point of Natural Invulnerability grants resistance to the next effect that would inflict a Wound, Death, State, or other negative effect, and is then removed. Does not trigger against effects cast by the player. Natural Invulnerability is the only type of armor that stacks with other armor types and is affected only after other armor types have been destroyed or are ineffective against the attack. Natural Invulnerability may not itself be the target of magic or abilities and may not be healed unless otherwise specified. Natural Invulnerability is never bypassed by Phase Arrow, Phase Bolt, or other similar abilities and is not ignored by abilities that ignore armor.